WorldPartitionRuntimeHashSet was set by default for me.
I have also just gone through your tutorial but without success. The same errors are still displayed. I also clicked on the link and read through the whole conversation you had with him and tried to implement it in exactly the same way, but also without success.
I just applied an old snapshot to see if the problem existed back then and yes, the error did exist back then. However, only trees are displayed as errors and not walls etc. What could be the reason for this?